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Bryan Sorenson, Thomas W. Kernozek, John David Willson, Robert Ragan and Jordan Hove

Context:

Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the “gold standard” for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative.

Objective:

To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study.

Participants:

31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]).

Methods:

Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements.

Results:

2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r 2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r 2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r 2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r 2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r 2 = .52), which was strengthened with the addition of hip sagittal-plane position (r 2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r 2 = .70).

Conclusion:

2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.

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Thomas W. Kernozek, Naghmeh Gheidi, Matthew Zellmer, Jordan Hove, Becky L. Heinert and Michael R. Torry

Context: Squatting is a common rehabilitation training exercise for patellofemoral pain syndrome (PFPS). Patellofemoral joint stress (PFJS) during squatting with more anterior knee displacement has not been systematically investigated. Objective: To compare PFJS during squatting using 2 techniques: squat while keeping the knees behind the toes (SBT) and squat while allowing the knees to go past the toes (SPT). Setting: University research laboratory. Participants: Twenty-five healthy females (age: 22.69 (0.74) y; height: 169.39 (6.44) cm; mass: 61.55 (9.74) kg) participated. Main Outcome Measures: Three-dimensional kinematic and kinetic data were collected at 180 and 1800 Hz, respectively. A musculoskeletal model was used to calculate muscle forces through static optimization. These muscle forces were used in a patellofemoral joint model to estimate PFJS. Results: The magnitudes of PFJS, reaction force, and quadriceps force were higher (P < .001) during SPT compared with the SBT technique. Knee flexion, hip flexion, and ankle dorsiflexion angles were reduced when using the SBT technique. Conclusions: Findings provide some general support for minimizing forward knee translation during squats for patients that may have patellofemoral pain syndrome.